Liquid paint is essentially a suspension of finely divided pigment particles in a liquid vehicle composed of a resin or binder and a volatile solvent. After the paint is applied the volatile solvent evaporates from the drying film and the binder holds the pigment in the dry film and causes it to adhere to the substrate.
There are two basic types of paints, referred to as water emulsion based and oil based. Water emulsion based paints, often referred to as latex paints, are composed of suspension of pigment particles and finely divided emulsified synthetic polymers in water. After the paint is applied to the substrate, the water evaporates from the drying film and the particles coalesce into a continuous film which acts as the pigment binder and adheres to the substrate. Oil based paints are composed of a dispersion of pigment particles in an oil based vehicle, such as an alkyd resin, in a solvent of mineral spirits. An alkyd resin is the reaction product of a polybasic acid (such as phthalic acid) and a polyhydric alcohol (for example, glycerol). Alkyds can be produced from a wide variety of polybasic acids, polyhydric alcohols, and monobasic fatty acids available in numerous molecular weight distributions.
In the manufacture of both oil and water based paints, pigments are suspended in the liquid phase of the paint compositions. Many of the pigments used in paints are difficult to disperse and suspend in the liquid phase. Iron oxides, for example, are highly charged particles which tend to agglomerate when suspended in liquids. Some of the other organic pigments used in paints are also difficult to suspend and disperse because of their molecular configuration. It is known to coat or encapsulate pigment particles to modify surface characteristics using certain polymeric materials. This practice is quite expensive, however, and adds a substantial cost to the final product. There remains a need for improved methods of suspending and dispersing pigments in industrial coating compositions such as paints, lacquers, and varnishes.
It is known in the prior art that certain polymers such as polytetrafluoroethylene (PTFE), polypropylene, polyethylene, etc. are capable of fibrillation.
Fibrillated polymers have been used to support various particulates. For example, in U.S. Pat. Nos. 4,938,952 and 5,093,110 to Kamen, fibrillated polymers are used to support cosmetic pigments in cosmetic compositions. U.S. Pat. No. 3,838,092 discloses the use of fibrillated polymers to pelletize solid particulate matter such as dust. U.S. Pat. No. 4,971,697 discloses sorptive silica particles enmeshed in a matrix of fibrillated polymer for use in chromatographic procedures.
It has most unexpectedly been discovered that pigments may be dispersed and suspended quite effectively in industrial coating compositions such as paints, lacquers, and varnishes by embedding the pigment in a fibrillated polymer network.